If the global population goes on increasing at its present rate, by the middle of the 21st century, we（  ）all our oil reserves.

If the global population goes on increasing at its present rate, by the middle of the 21st century, we（  ）all our oil reserves.

A.

will have used up

B.

are using up

C.

will have been using up

D.

have used up

正确答案是A